Adamantane 11-beta-HSD-1 inhibitors: Application of an isocyanide multicomponent reaction

Mono- and Diamination of 4,6-Dichloropyrimidine, 2,6-Dichloropyrazine and 1,3-Dichloroisoquinoline with Adamantane-Containing Amines

N-heteroaryl substituted adamantane-containing amines are of substantial interest for their perspective antiviral and psychotherapeutic activities. Chlorine atom at alpha-position of N-heterocycles has been substituted by the amino group using convenient nucleophilic substitution reactions with a series of adamantylalkylamines. The prototropic equilibrium in these compounds was studied using NMR spectroscopy. The introduction of the second amino substituent in 4-amino-6-chloropyrimidine, 2-amino-chloropyrazine, and 1-amino-3-chloroisoquinoline was achieved using Pd(0) catalysis.

Synthesis, in vitro cytotoxic and apoptotic effects, and molecular docking study of novel adamantane derivatives

[4-(Adamantane-1-carboxamido)-3-oxo-1-thia-4-azaspiro[4.4]nonan-2-yl]acetic acid (4a) and [4-(adamantane-1-carboxamido)-8-nonsubstituted/substituted-3-oxo-1-thia-4-azas-piro[4.5]decane-2-yl]acetic acid (4b-g) derivatives were synthesized; their structures were verified by elemental analysis, infrared spectroscopy, ¹ H nuclear magnetic resonance (NMR), ¹³ C NMR, and mass spectroscopy data; and their in vitro cytotoxicity activities were investigated against human hepatocellular carcinoma, human prostate adenocarcinoma, and human lung carcinoma cell lines (HepG2, PC-3, and A549, respectively), and a mouse fibroblast cell line (NIH/3T3). All compounds, except compound 4e, were found as cytotoxic, especially on A549 cells as compared with the other cells (selectivity index = 2.01-11.6). As a further step, the effects of compounds 4a-c on apoptosis induction were tested and the expression of selected apoptosis genes was analyzed. Among the selected compounds, compound 4a induced apoptosis remarkably. Moreover, computational calculations of the binding of compounds 4a-c to the BIR3 domain of the human inhibitor of apoptosis protein revealed ligand-protein interactions at the atomistic level and emphasized the importance of a hydrophobic moiety on the ligands for better binding.

A Novel 18F-Labeled Radioligand for Positron Emission Tomography Imaging of 11β-Hydroxysteroid Dehydrogenase (11β-HSD1): Synthesis and Preliminary Evaluation in Nonhuman Primates

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) catalyzes the conversion of cortisone to cortisol and controls a key pathway in the regulation of stress. Studies have implicated 11β-HSD1 in metabolic diseases including type 2 diabetes and obesity, as well as stress-related disorders and neurodegenerative diseases, such as depression and Alzheimer's disease (AD). We have previously developed [¹¹C]AS2471907 as a PET radiotracer to image 11β-HSD1 in the brain of nonhuman primates and humans. However, the radiosynthesis of [¹¹C]AS2471907 was unreliable and low-yielding. Here, we report the development of the ¹⁸F-labeled version [¹⁸F]AS2471907, including the synthesis of two iodonium ylide precursors and the optimization of ¹⁸F-radiosynthesis. Preliminary PET experiments, composed of a baseline scan of [¹⁸F]AS2471907 and a blocking scan with the reversible 11β-HSD1 inhibitor ASP3662 (0.3 mg/kg), was also conducted in a rhesus monkey to verify the pharmacokinetics of [¹⁸F]AS2471907 and its specific binding in the brain. The iodonium ylide precursors were prepared in a seven-step synthetic route with an optimized overall yield of ∼2%. [¹⁸F]AS2471907 was synthesized in good radiochemical purity, with the ortho regioisomer of iodonium ylide providing greater radiochemical yield as compared with the para regioisomer. In monkey brain, [¹⁸F]AS2471907 displayed high uptake and heterogeneous distribution, while administration of the 11β-HSD1 inhibitor ASP3662 significantly reduced radiotracer uptake, thus demonstrating the binding specificity of [¹⁸F]AS2471907. Given the longer half-life of F-18 and feasibility for central production and distribution, [¹⁸F]AS2471907 holds great promise to be a valuable PET radiotracer to image 11β-HSD1 in the brain.

Design, synthesis, and biological evaluation of novel selective peptide inhibitors of 11β-hydroxysteroid dehydrogenase 1

The enzyme 11β-HSD1 plays a crucial role in the tissue-specific regulation of cortisol levels and it has been associated with various diseases. Inhibition of 11β-HSD1 is an attractive intervention strategy and the discovery of novel selective 11β-HSD1 inhibitors is of high relevance. In this study, we identified and evaluated a new series of selective peptide 11β-HSD1 inhibitors with potential for skin care applications. This novel scaffold was designed with the aid of molecular modeling and two previously reported inhibitors. SAR optimization yielded highly active peptides (IC₅₀ below 400 nM) that were inactive at 1 µM concentration against structurally related enzymes (11β-HSD2, 17β-HSD1 and 17β-HSD2). The best performing peptides inhibited the conversion of cortisone into cortisol in primary human keratinocytes and the most active compound, 5d, was further shown to reverse cortisone-induced collagen damage in human ex-vivo tissue.

Design, synthesis and in vivo study of novel pyrrolidine-based 11β-HSD1 inhibitors for age-related cognitive dysfunction

Recent findings suggest that treatment with 11β-HSD1 inhibitors provides a novel approach to deal with age-related cognitive dysfunctions, including Alzheimer's disease. In this work we report potent 11β-HSD1 inhibitors featuring unexplored pyrrolidine-based polycyclic substituents. A selected candidate administered to 12-month-old SAMP8 mice for four weeks prevented memory deficits and displayed a neuroprotective action. This is the first time that 11β-HSD1 inhibitors have been studied in this broadly-used mouse model of accelerated senescence and late-onset Alzheimer's disease.

Asymmetric 18F-fluorination for applications in positron emission tomography

Positron emission tomography (PET) is becoming more frequently used by medicinal chemists to facilitate the selection of the most promising lead compounds for further evaluation. For PET, this entails the preparation of 11C- or 18F-labeled drugs or radioligands. With the importance of chirality and fluorine substitution in drug development, chemists can be faced with the challenge of preparing enantiopure molecules featuring the 18F-tag on a stereogenic carbon. Asymmetric 18F-fluorination is an emerging field of research that provides an alternative to resolution or conventional SN2-based radiochemistry. To date, both transition metal complexes and organomediators have been successfully employed for 18F-incorporation at a stereogenic carbon.

Methods to Increase the Metabolic Stability of (18)F-Radiotracers

The majority of pharmaceuticals and other organic compounds incorporating radiotracers that are considered foreign to the body undergo metabolic changes in vivo. Metabolic degradation of these drugs is commonly caused by a system of enzymes of low substrate specificity requirement, which is present mainly in the liver, but drug metabolism may also take place in the kidneys or other organs. Thus, radiotracers and all other pharmaceuticals are faced with enormous challenges to maintain their stability in vivo highlighting the importance of their structure. Often in practice, such biologically active molecules exhibit these properties in vitro, but fail during in vivo studies due to obtaining an increased metabolism within minutes. Many pharmacologically and biologically interesting compounds never see application due to their lack of stability. One of the most important issues of radiotracers development based on fluorine-18 is the stability in vitro and in vivo. Sometimes, the metabolism of ¹⁸F-radiotracers goes along with the cleavage of the C-F bond and with the rejection of [¹⁸F]fluoride mostly combined with high background and accumulation in the skeleton. This review deals with the impact of radiodefluorination and with approaches to stabilize the C-F bond to avoid the cleavage between fluorine and carbon.

Novel 11β-HSD1 inhibitors: C-1 versus C-2 substitution and effect of the introduction of an oxygen atom in the adamantane scaffold

The adamantane scaffold is found in several marketed drugs and in many investigational 11β-HSD1 inhibitors. Interestingly, all the clinically approved adamantane derivatives are C-1 substituted. We demonstrate that, in a series of paired adamantane isomers, substitution of the adamantane in C-2 is preferred over the substitution at C-1 and is necessary for potency at human 11β-HSD1. Furthermore, the introduction of an oxygen atom in the hydrocarbon scaffold of adamantane is deleterious to 11β-HSD1 inhibition. Molecular modeling studies provide a basis to rationalize these features.

Benzimidazole-2-one: a novel anchoring principle for antagonizing p53-Mdm2

Herein we propose the benzimidazole-2-one substructure as a suitable tryptophan mimic and thus a reasonable starting point for the design of p53 Mdm2 antagonists. We devise a short multicomponent reaction route to hitherto unknown 2-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)acetamides by reacting mono N-carbamate protected phenylenediamine in a Ugi-3CR followed by base induced cyclisation. Our preliminary synthesis and screening results are presented here. The finding of the benzimidazolone moiety as a tryptophan replacement in mdm2 is significant as it offers access to novel scaffolds with potentially higher selectivity and potency and improved biological activities. Observing low μM affinities to mdm2 by NMR and fluorescence polarization we conclude that the 2-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)acetamide scaffold might be a good starting point to further optimize the affinities to Mdm2.

Investigations into the synthesis, radiofluorination and conjugation of a new [¹⁸F]fluorocyclobutyl prosthetic group and its in vitro stability using a tyrosine model system

The [(18)F]fluorocyclobutyl group has the potential to be a metabolically stable prosthetic group for PET tracers. The synthesis of the radiolabeling precursor cis-cyclobutane-1,3-diyl bis(toluene-4-sulfonate) 8 was obtained from epibromohydrin in 7 steps (2% overall yield). The radiolabeling of this precursor 8 and its conjugation to L-tyrosine as a model system was successfully achieved to give the new non-natural amino acid 3-[(18)F]fluorocyclobutyl-L-tyrosine (L-3-[(18)F]FCBT) [(18)F]17 in 8% decay-corrected yield from the non-carrier-added [(18)F]fluoride. L-3-[(18)F]FCBT was investigated in vitro in different cancer cell lines to determine the uptake and stability. The tracer [(18)F]17 showed a time dependent uptake into different tumor cell lines (A549, NCI-H460, DU145) with the best uptake of 5.8% injected dose per 5×10(5) cells after 30min in human lung carcinoma cells A549. The stability of L-3-[(18)F]FCBT in human and rat plasma and the stability of the non-radioactive L-3-FCBT in rat hepatocytes were both found to be excellent. These results show that the non-natural amino acid L-3-[(18)F]FCBT is a promising metabolically stable radiotracer for positron emission tomography.

Koch-Haaf reaction of adamantanols in an acid-tolerant hastelloy-made microreactor

The Koch–Haaf reaction of adamantanols was successfully carried out in a microflow system at room temperature. By combining an acid-tolerant hastelloy-made micromixer, a PTFE tube, and a hastelloy-made microextraction unit, a packaged reaction-to-workup system was developed. By means of the present system, the multigram scale synthesis of 1-adamantanecarboxylic acid was achieved in ca. one hour operation.

Inhibitors of 11β-hydroxysteroid dehydrogenase type 1 in antidiabetic therapy

Glucocorticoid action is mediated by glucocorticoid receptor (GR), which upon cortisol binding is activated and regulates the transcriptional expression of target genes and downstream physiological functions. 11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) catalyzes the conversion of inactive cortisone to active cortisol. Since cortisol is also produced through biosynthesis in the adrenal glands, the total cortisol level in a given tissue is determined by both the circulating cortisol concentration and the local 11β-HSD1 activity. 11β-HSD1 is expressed in liver, adipose, brain, and placenta. Since it contributes to the local cortisol levels in these tissues, 11β-HSD1 plays a critical role in glucocorticoid action. The metabolic symptoms caused by glucocorticoid excess in Cushing's syndrome overlap with the characteristics of the metabolic syndrome, suggesting that increased glucocorticoid activity may play a role in the etiology of the metabolic syndrome. Consistent with this notion, elevated adipose expression of 11β-HSD1 induced metabolic syndrome-like phenotypes in mice. Thus, 11β-HSD1 is a proposed therapeutic target to normalize glucocorticoid excess in a tissue-specific manner and mitigate obesity and insulin resistance. Selective inhibitors of 11β-HSD1 are under development for the treatment of type 2 diabetes and other components of the metabolic syndrome.

Multicomponent reactions of cyclobutanones

Cyclobutanones are essentially unknown as reactants in isonitrile-based multicomponent reactions. Ugi reactions of cyclobutanone and Passerini reactions of tetramethylcyclobutane-1,3-dione have been performed in this work. These reactions are significantly enhanced by being conducted in water, a subject of recent interest whose basis is still in question but whose effects are beyond doubt. The Ugi reaction of cyclobutanone has been used in a brief synthesis of an aspartame analogue.

Discovery and biological evaluation of adamantyl amide 11beta-HSD1 inhibitors

A series of adamantyl amide 11beta-HSD1 inhibitors has been discovered and chemically modified. Selected compounds are selective for 11beta-HSD1 over 11beta-HSD2 and possess excellent cellular potency in human and murine 11beta-HSD1 assays. Good pharmacodynamic characteristics are observed in ex vivo assays.